I. Definitions
As used herein, the phrase “group III-V” refers to a compound semiconductor including at least one group III element and at least one group V element. By way of example, a group III-V semiconductor may take the form of a III-Nitride semiconductor. “III-Nitride” or “III-N” refers to a compound semiconductor that includes nitrogen and at least one group III element including aluminum (Al), gallium (Ga), indium (In), and boron (B), and including but not limited to any of its alloys, such as aluminum gallium nitride (AlxGa(1-x)N), indium gallium nitride (InyGa(1-y)N), aluminum indium gallium nitride (AlxInyGa(1-x-y)N), gallium arsenide phosphide nitride (GaAsaPbN(1-a-b)), aluminum indium gallium arsenide phosphide nitride (AlxInyGa(1-x-y)AsaPbN(1-a-b)), for example. III-Nitride also refers generally to any polarity including but not limited to Ga-polar, N-polar, semi-polar, or non-polar crystal orientations. A III-Nitride material may also include either the Wurtzitic, Zincblende, or mixed polytypes, and may include single-crystal, monocrystalline, polycrystalline, or amorphous structures. Gallium nitride or GaN, as used herein, refers to a III-Nitride compound semiconductor wherein the group III element or elements include some or a substantial amount of gallium, but may also include other group III elements in addition to gallium.
Also as used herein, the phrase “group IV” refers to a semiconductor that includes at least one group IV element such as silicon (Si), germanium (Ge), and carbon (C), and also includes compound semiconductors such as silicon germanium (SiGe) and silicon carbide (SiC), for example. Group IV also refers to semiconductor materials which include more than one layer of group IV elements, or doping of group IV elements to produce strained group IV material, and may also include group IV based composite substrates such as silicon on insulator (SOI), separation by implantation of oxygen (SIMOX) process substrates, and silicon on sapphire (SOS), for example.
Moreover, and as also used herein, the phrase “LV transistor” refers to a low-voltage transistor, while the phrase “HV transistor” refers to a high-voltage transistor. Typical voltage ratings include LV˜0V-50V, midvoltage (MV)˜50V-300V, and HV˜300V-1200V.
II. Background Art
In high power and high performance circuit applications, group III-V transistors, such as III-Nitride field-effect transistors (FETs) and high mobility electron transistors (HEMTs), are often desirable for their high efficiency and high-voltage handling capability. Moreover, it is often desirable to combine such III-Nitride transistors with other FETs, such as silicon FETs, to create high performance composite switches.
In applications for which normally OFF switches are desirable, a depletion mode (normally ON) III-Nitride transistor can be cascoded with an enhancement mode (normally OFF) low-voltage (LV) group IV transistor to produce an enhancement mode (normally OFF) composite switch. However, conventional techniques for combining Nitride transistors with silicon FETs, for example, often offset the benefits provided by III-Nitride transistors. For instance, conventional composite designs may place the III-Nitride transistor and silicon FET side-by-side on a common support surface. Such a side-by-side configuration can undesirably increase the parasitic inductance and resistance in the current paths of the composite switch.